NavList:

Bill Lionheart you wrote:

Do we know of any techniques in celestial navigation that were kept
secret by a government, navy (or in the 20th C air force) at the time?
One would think some ideas were good enough to give a tactical
advantage in war.

Not just between governments and navies, armies and air forces.  Such is the spirit of competition in the armed forces, that there might be, not quite secrecy but, certainly a reticence to communicate promising techniques between, ships, regiments, commands, wings, squadrons, and even individual crews.  Was this secrecy, or was it just everyone thought the method they’d got used to best, and did this attitude stifle true innovation?  E.g.  I found out as recently as this year that in the 1960s prior to competition, with respect to DR errors, while most squadrons were compass swinging their aircraft on the ground towed behind a massive steel tractor using a massive steel tow-bar, the aircraft at one station were being swung in the air using the Sun and a Vernier scales attached to the periscopic sextant heading ring.  Magnetic variation at the time and place of swing was provided by the Admiralty Compass Observatory.  That never percolated though, possibly because it was complicated, expensive, and mabe not much better.  On the other hand, innovations like the five and seven shot sandwich fix and the Mear’s slide for correcting acceleration errors were taken up Command wide fairly quickly. What about the US star trackers?  I should think they had quite a high security classification initially.  DaveP